1. Field of the Invention
The present invention relates to a zoom lens usable as a photographing lens of a lens shutter camera and a photographing lens of a video camera.
2. Description of the Related Art
Recently, a zoom lens has been mostly mounted onto a lens shutter camera. A new problem of how to make the camera having the zoom lens compact is caused.
When the camera is made compact, a maximum problem from a viewpoint of portability of the camera is to reduce a size of the camera in an optical axis direction of the zoom lens. Namely, this maximum problem is to make the zoom lens thin.
Recently, the lens shutter camera mounting the zoom lens thereon is made thin by increasing the number of stages in body tube. However, it is important to make the zoom lens itself thin. In particular, an entire length of the lens shutter camera at a long focal end (a distance from a lens front end to an image face) and an entire thickness of all movable lens groups at a most approaching time thereof (a distance from a lens front end to a lens rear end) are most important as a factor for determining thinness of the camera.
A zoom lens constructed by two lens groups as shown in Japanese Patent Application Laying Open (KOKAI) No. 5-11186 is generally known as a zoom lens having a relatively short length as the above entire lens length. A zoom lens constructed by two lens groups as shown in Japanese Patent Application Laying Open (KOKAI) No. 5-127082 is known as a zoom lens having a relatively thin thickness as the entire lens group thickness.
An entire length of the former zoom lens ranges from 0.96 to 0.92 times the focal length of an entire lens system at a long focal end so that this entire length of the former zoom lens is short. However, the entire lens group thickness of the former zoom lens is about 1.25 times the height of a maximum image. This entire lens group thickness is thick and is still insufficient to make the camera thin.
An entire lens group thickness of the latter zoom lens at a long focal end is approximately equal to the height of a maximum image so that the latter zoom lens is suitable for making the camera thin. However, a zoom ratio as an important factor is a small value such as about 1.6 magnifications so that the latter zoom lens is not necessarily practical.